AB0649 PERIPHERAL B CELLS IMMUNOPHENOTYING IN SYSTEMIC LUPUS ERYTHEMATOSUS PATIENTS
Authors: C. DI Mario, V. Varriano, L. Petricca, A. Paglionico, M. R. Gigante, B. Tolusso, E. Gremese
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> B cells play a central role in systemic lupus erythematosus (SLE) pathogenesis connecting innate with adaptative immunity. <h3>Objectives</h3> To investigate the peripheral blood B cell phenotype in a cohort of SLE patients with renal (LN-SLE) and non-renal (NR-SLE) involvement compared to healthy controls. <h3>Methods</h3> Ninety-nine SLE patients, 76 with active renal involvement (30 at disease onset-Early and 46 in whom LN occurred after the disease onset-Long) and 23 with non-renal disease (articular and/or cutaneous) were enrolled. Thirty-seven healthy controls were included. Clinical, laboratory and demographic data were collected at baseline and at 6 and 12 months of follow-up. Disease activity was recorded using SLEDAI-2K. The memory B cells immunophenotyping (IgD/CD27 classification) was analyzed in peripheral blood through flow cytometry. To clarify the role of key molecules in the B cells activation, IL-6 and BAFF serum levels were assayed by Enzyme-linked immunosorbent assay (ELISA). <h3>Results</h3> Studying the B cell subsets, a lower percentage of CD19<sup>pos</sup> and unswitched memory (IgD<sup>pos</sup>CD27<sup>pos</sup>) in the whole SLE cohort compared to controls (8.7±6.8% <i>vs</i> 10.5±3.5%; <i>p=0.002</i> and 10.7±13.7% <i>vs</i> 15.3±8.0%; <i>p</i>&lt;<i>0.01,</i> respectively) was observed. In addition, we found higher levels of double-negative memory B cells (IgD<sup>neg</sup>CD27<sup>neg</sup>) and plasmablasts (CD27<sup>pos</sup>CD38<sup>pos</sup>) in SLE than in controls [(CD27<sup>neg</sup>IgD<sup>neg</sup> 10.3±8.3% <i>vs</i> 4.1±1.9%; <i>p&lt;0.01</i>) (CD27<sup>pos</sup>CD38<sup>pos</sup> 6.1±7.9% <i>vs</i> 1.0±0.5%; <i>p</i>&lt;<i>0.01</i>)]. Furthermore, CD19<sup>pos</sup> negatively correlated with BAFF (R=-0.322; <i>p=0.01</i>). No correlation was found between B cell subsets and the disease activity parameters. According to the organ involvement, LN-SLE and RN-SLE showed a lower percentage of CD19<sup>pos</sup>, IgD<sup>pos</sup>CD27<sup>pos</sup> and plasmacells and higher levels of IgD<sup>neg</sup>CD27<sup>neg</sup> than controls [(CD19<sup>pos</sup>: LN-SLE:9.1±7.4% <i>vs</i> 10.5±4.6%; <i>p=0.005;</i> NR-SLE: 7.7±4.6%; <i>p=0.008</i>)(IgD<sup>pos</sup>CD27<sup>pos</sup>:LN-SLE 10.4±14.9% <i>vs</i> 15.3±8.0%; <i>p</i>&lt;<i>0.001;</i> NR-SLE: 11.8±8.6%; <i>p=0.006</i>) (CD27<sup>pos</sup>CD38<sup>pos</sup>: LN-SLE 7.5±8.4% <i>vs</i> 0.9±0.5%; <i>p</i>&lt;<i>0.001;</i> NR-SLE: 1.6±2.2%; <i>p</i>=<i>0.001</i>)(IgD<sup>neg</sup>CD27<sup>neg</sup>: LN-SLE 10.6±8.5% <i>vs</i> 4.1±1.9%; <i>p</i>&lt;<i>0.001;</i> NR-SLE: 9.6±7.3%; <i>p=0.006</i>]. According to the onset of renal symptoms, there were no differences in the distribution of the renal classes and in activity and chronicity indexes in the two groups. Analyzing the B cells subsets the Long-LN-SLE showed a lower percentage of CD19<sup>pos</sup> and unswitched memory (IgD<sup>pos</sup>CD27<sup>pos</sup>) compared to controls (8.6±6.5% <i>vs</i> 10.5±3.5%; <i>p=0.004</i> and 9.7±6.9% <i>vs</i> 15.3±8.0%;<i>p=0.001,</i> respectively) and higher levels of IgD<sup>neg</sup>CD27<sup>neg</sup> (12.1±8.4%) than Early LN-SLE (8.3±8.3%;p<i>=0.027</i>), NR-SLE (9.6±7.3%;p<i>=0.001</i>) and controls(4.1±1.9%;p&lt;<i>0.001</i>). Furthermore, a direct correlation was observed between serum IL-6 levels and SLEDAI in Long-LN-SLE patients (r=0.380; p=0.004). <h3>Conclusion</h3> Data on memory B cells immunophenotyping reveals a distinct B cells subset of SLE patients when compared to healthy controls, confirming an alteration of B cells subsets in SLE patients and strengthening the hypothesis of the pathogenetic role played by B lymphocytes in the course of LN. In particular, the higher levels of DN B cells observed in patients in which renal damage occurs after the onset of SLE reinforcing the data that these cells represents a B memory subsets characteristic of immune system overactivation conditions. <h3>Reference</h3> [1]Sang A, Zheng YY, Morel L Contributions of B cells to lupus pathogenesis. <i>Mol Immunol</i> 2014; 62 (2): 329–338 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.